This invention relates to aircraft blades, and in particular, to an improvement in an apparatus for continuously detecting cracks in propeller and helicopter rotor blades.
Aircraft blades are subjected to severe stress and occasionally develop minute cracks. It is of critical importance that a crack in the blade be detected at an early time so that the blade may be replaced preventing an inflight accident. A wide variety of methods are available for detecting cracks, including the making of x-ray pictures, magnetic flux techniques, and detection of pressure changes within a sealed hollow blade.
A method and apparatus utilizing a blade pressure sensor is disclosed in U.S. Pat. No. 3,985,318, and the present invention is an improvement on that system.
The prior art system is illustrated in FIG. 1 which shows a conventional helicopter with a plurality of rotor blades 10. A pressure sensor 11 with a beta radiation source is mounted in each of the blades. A beta radiation detector 12 is mounted on a fixed portion of the aircraft adjacent the rotating blades. The system also includes a signal processor 13 containing electronic circuitry, and a warning indicator 14 for mounting on the instrument panel of the aircraft.
The typical pressure sensor 11 includes a member which moves as a function of the pressure within the blade on which the sensor is mounted. A beta radiation source is carried on the moving member and a radiation shield or window is provided in the sensor so that radiation from the source is blocked when the pressure on the blade is in an acceptable range, and radiation passes the shield or window when the pressure is in an unacceptable range, thereby indicating leakage through a crack in the blade. This prior art system is described in greater detail in the aforesaid U.S. Pat. No. 3,985,318. The present invention is directed to a new and improved housing for the beta radiation detector.
The radiation detector is mounted on the aircraft in a position for receiving radiation from a sensor. However, modern day aircraft are exposed to many types of radiation including electromagnetic radiation in the microwave range produced by high power radar systems and the like. These extraneous radiation sources can adversely affect the operation the crack detection system when received by the radiation detector. The present invention provides a new and improved beta radiation detector housing which substantially eliminates detector sensitivity to radar transmissions and other transmissions in the electromagnetic region, while maintaining detector sensitivity to nuclear beta radiation.